C (g) + O2 (g) → CO2 (g) ΔH = -393.5 kJ How much energy is involved when 88.0 grams of CO2 is synthesized?

Question

C (g) + O2 (g) → CO2 (g)  ΔH = -393.5 kJ

How much energy is involved when 88.0 grams of CO2 is synthesized?

Answer 1

Hello, Jenn,

I'm wondering if the enthalpy you've provided has the correct units. It needs to include an amount (moles, kg, etc.) to be a useful number. I suspect the correct units are kJ/mole CO₂. I'll use this unit to illustrate how we can calculate the energy involved when 88.0 grams of CO₂ is synthesized.

C (g) + O2 (g) → CO2 (g) ΔH = -393.5 kJ/mole CO₂

Now we can see that we need to know how many moles were synthesized to use the enthalpy u niy. The molar mass of CO₂ is (12+16+16) 44 g/mole. So 88.0 grams would be 2.00 moles of CO₂.

[Since we are given 88.0 grams, or exactly 2 moles, I can take some comfort in that we may on the right track. Not a coincidence, right?]

Now we can find the energy:

(2 moles CO₂)*(-393.5kJ/mole CO₂) = -787 kJ (3 sig figs). The minus sign tells us that energy is released in this reaction.

Bob